a(n) = n^2*(n^2 - 1)/4.

Terms

a(0) =0a(1) =0a(2) =3a(3) =18a(4) =60a(5) =150a(6) =315a(7) =588a(8) =1008a(9) =1620a(10) =2475a(11) =3630a(12) =5148a(13) =7098a(14) =9555a(15) =12600a(16) =16320a(17) =20808a(18) =26163a(19) =32490a(20) =39900a(21) =48510a(22) =58443a(23) =69828a(24) =82800a(25) =97500a(26) =114075a(27) =132678a(28) =153468a(29) =176610